Lead air control apparatus of stratified scavenging two-cycle engine

ABSTRACT

In an insulator ( 21 ) inserted between a carburetor ( 30 ) and a cylinder ( 3 ) for a purpose of insulating heat, there are formed an intake passage ( 22 ) connected to the carburetor ( 30 ), and a pair of first air passages ( 23 ) connected to respective air flow paths ( 14 ) communicated with a pair of scavenging ports ( 10 ) formed in the cylinder ( 3 ). Air control valves ( 25 ) are respectively provided within a pair of first protruding portions ( 33 ) communicating with an air cleaner ( 32 ), and are connected to the pair of first air passages ( 23 ) via a pair of connection members ( 35 ). Portions from the air passages within the pair of first protruding portions ( 33 ) to the pair of first air passages ( 23 ) are respectively formed as smooth air passages in which a change of an inner diameter cross sectional area in a connection portion is small.

TECHNICAL FIELD

The present invention relates to a lead air control apparatus forcontrolling an air amount of a lead air for scavenging of a stratifiedscavenging two-cycle engine.

BACKGROUND ART

In conventional, there has been proposed various configurations as astratified scavenging two-cycle engine having an air control valvecontrolling an air amount of a scavenging lead air. For example, therehas been proposed a lead air control apparatus of a stratifiedscavenging two-cycle engine, as described in Japanese Patent ApplicationLaid-Open (JP-A) No. 2000-328945.

The lead air control apparatus described in JP-A No. 2000-328945 isshown in FIG. 9. As shown FIG. 9, in a stratified scavenging two-cycleengine 40, a pair of scavenging ports 10 are provided in opposing bothside surface portions, on an inner wall surface of a cylinder 3 to whicha piston 4 is slidably fitted, and a pair of scavenging ports 10 arerespectively connected to a crank chamber 11 by scavenging flow paths12.

A carburetor 42 is attached to an intake port 13 provided in thecylinder 3 via an insulator 41 aiming at a heat insulation, and anintake side of the carburetor 42 is connected to an air cleaner 44. Thecarburetor 42 is provided with a butterfly type throttle valve 43. Theinsulator 41 is provided with an intake passage 22 connecting the intakeport 13 and the carburetor 42, and an air passage 45 for the lead air.

One side of the air passage 45 for the lead air is connected to the aircleaner 44, and the other end thereof is formed in a fork shape so as tobe branched into right and left sides, which are respectively connectedto the pair of scavenging ports 10 and the scavenging flow paths 12 viaconnection pipes 46. A butterfly type air control valve 25 controllingthe air amount of the lead air is provided in an upstream side of thebranch point of the air passage 45, and is configured such as to workwith the throttle valve 43 of the carburetor 42.

Accordingly, it is possible to attach the air control valve 25 within alimited space, it is possible to make an entire length M of the engineshort, and it is possible to achieve a compact and light configuration.

However, in the configuration described in JP-A No. 2000-328945, the aircontrol valve is provided in the air passage arranged in the insulator,the air passage is branched into the right and left sides in adownstream portion of the air control valve, and the branched airpassages are respectively connected to the pair of scavenging ports anda pair of scavenging flow paths which are provided in the left and rightsides of the cylinder of the engine. Accordingly, the configuration ofthe insulator is complicated, and the length of the insulator iselongated, and a large area product is required. As a result, an outerdiameter of the engine is increased.

Further, a configuration for easily forming the air passage can beachieved by forming the air passage formed within the insulatorapproximately in a linear shape. Accordingly, when the air passage isconfigured so as to be branched into the right and left sides within theinsulator, it becomes complicated to form the branched air passage, andan elbow shape, that is, a shape in which the linear air passages cross,is formed at the branch portion in the air passage. If the air passageis formed in a sharply bent shape at the branch portion, there is aproblem that the air flow in the bent portion forms a flow in which avortex flow is generated by being peeled off from the inner wall of theair passage, whereby an air resistance is increased.

DISCLOSURE OF THE INVENTION

The present invention is made by taking the problem mentioned above intoconsideration, and an object of the present invention is to provide alead air control apparatus of a stratified scavenging two-cycle enginein which a flow resistance of a lead air is small, and a simple andcompact configuration is achieved.

In order to achieve the object mentioned above, according to a mostprincipal aspect of the present invention, there is provided astratified scavenging two-cycle engine comprising: a pair of first airpassages formed in an insulator inserted between a carburetor and acylinder for a purpose of heat insulation, and respectively connected toa pair of scavenging ports provided in the cylinder; a pair of secondair passages respectively connecting between an air cleaner and therespective first air passages, and arranged in an approximately parallelstate; and an air control valve controlling an air amount of a lead airfor scavenging.

Accordingly, it is possible to configure the air passage of the lead airformed by connecting the pair of second air passages respectivelyprovided with the air control valves to the pair of first air passagesformed in the insulator, as the approximately parallel arranged airpassages. Further, it is not necessary that the air passage for the leadair is configured such that the passage is branched into right and leftsides by arranging the branch portion in the middle of the air passage.Further, as the air passage formed within the insulator, the first airpassages can be formed as a pair of independent air passages.

Accordingly, it is not necessary to form the sharply bent elbow portionwithin the air passage of the lead air. Further, since the sharply bentelbow portion does not exist within the air passage of the lead air, itis possible to smoothly circulate the air within the air passage of thelead air, and it is possible to reduce the air resistance within the airpassage of the lead air. Further, it is possible to improve an engineperformance by reducing an air resistance within the air passage of thelead air.

Further, it is possible to simplify the configuration of the first airpassage within the insulator, and it is possible to make the shape ofthe insulator compact. Accordingly, it is possible to configure anentire stratified scavenging two-cycle engine compact.

Further, it is possible to arrange the intake passage from thecarburetor and a pair of air passages of the lead air in a definitelysorting state. Accordingly, it is possible to prevent the air passage ofthe lead air and the intake passage from the carburetor from crossingeach other in the middle, and it is possible to prevent a pair of airpassages of the lead air from being arranged in both sides of the intakepassage of the carburetor, whereby the entire stratified scavengingtwo-cycle engine can be configured so as to be simple and compact.

In particular, it is possible to form the first air passage on the sameplane as the scavenging port, by arranging the air passage of the leadair above the intake passage from the carburetor, and it is possible toconfigure the air passage and the intake passage in a smooth connectionstate having a small air resistance. Accordingly, it is possible to keepthe entire length of the piston low, and to configure the entire lengthof the engine low, whereby the engine can be configured so as to becompact.

According to a main aspect of the present invention, the air controlvalve is provided near the air cleaner or is integrally formed with theair cleaner, a connection member connected to each of the first airpassages is provided in each of the second air passages, and an innerperipheral wall of the air passage from each first air passage up toeach second air passage is formed smoothly and continuously along alength direction of the air passage.

Accordingly, owing to the interposition of the connection member, evenif the connecting positions of the first air passage and the second airpassage are different, the first air passage and the second air passagecan be configured as the smooth continuous passages by the connectionmember. Further, since the inner peripheral wall of the air passage fromeach first air passage to each second air passages is formed smoothlyand continuously along the length direction of the air passage, it ispossible to reduce the air resistance of the lead air within the airpassage.

Since the first air passage and the second air passage are configured soas to have the arrangement mentioned above, it is possible to expand aninterval between the connection position of the second air passage andthe air cleaner, and the connection position of the carburetor and theair cleaner, so that a large size air cleaner can be used as the aircleaner. Accordingly, the large size air cleaner can be used for a smallsize engine by connecting the large size air cleaner to the small sizeengine, in which an intake port for an air-fuel mixture and an air flowpath for a lead air are arranged at close positions.

Further, since the connection member is employed for connecting the eachfirst air passage and each second air passage, the configuration of theinsulator is simple, and it is possible to manufacture the insulatorcompact and at a low cost. Further, it is possible to configure theentire stratified scavenging two-cycle engine compact, by forming theinsulator compact.

According to a main aspect of the present invention, a connectionportion in an end portion of the connection member is formed such that achange of an internal diameter cross sectional area is small between theconnection portion and a connected portion.

Accordingly, it is possible to connect the connection member and aconnected portion in a state in which the change of the inner diametercross sectional area is small between the connection member side and theconnected portion side, in the connection portion between an end portionof the connection member and the connected portion. Further, it ispossible to smoothly and continuously form the inner peripheral wall ofthe air passage from each first air passage to each second air passagealong the length direction of the air passage.

According to a main aspect of the present invention, the connectionmember has a flexibility. Accordingly, since the connection member hasthe flexibility, it is possible to configure the first air passage andthe second air passage as the smooth and continuous passage by theconnection member in a simple and easily assembled manner, even if theconnection positions of the first air passage and the second air passageare different.

According to a main aspect of the present invention, the respectivefirst air passages are arranged so as to be approximately parallel toeach other, and are formed as approximately linear air passages.

Accordingly, since it is possible to form the first air passage formedin the insulator as the independent approximately linear air passage, itis possible to form the first air passage in the insulator easily.Further, since the first air passage and the second air passage areconnected by the connection member having the flexibility, it ispossible to increase a freedom of selecting the position at which aninlet is formed in the first air passage, and it is possible to easilyconfigure the insulator.

As a result, it is possible to simplify the configuration of the entirestratified scavenging two-cycle engine, and it is possible to configurethe engine compact. Further, it is possible to configure the air passageof the lead air as the smooth air passage having the small airresistance.

The approximately linear air passage involves an air passage shape inwhich a center axial line of an air passage is formed in anapproximately linear shape such as an air passage shape in which aninner diameter within the air passage is expanded from an upstream sidetoward a downstream side, an air passage shape in which the innerdiameter is inversely compressed from the upstream side toward thedownstream side, and the like, in addition to the air passage in whichthe inner diameter is entirely uniform.

According to a main aspect of the present invention, each first airpassage has an air flow path formed within the cylinder, and the pair ofair flow paths and the pair of scavenging ports are arranged so as to beconnectable on the same plane.

Accordingly, it is possible to communicate the air flow path formedwithin the cylinder in the air passage of the lead air, with thescavenging port formed within the cylinder on the same plane, and it ispossible to linearly connect from the air flow path to the scavengingport.

The air flow path can be configured so as to be directly connected tothe scavenging port within the cylinder. Further, the air flow path canbe configured by the first air flow path formed within the cylinder andthe second air flow path formed on an outer peripheral surface of thepiston.

When the air flow path is formed by the first air flow path and thesecond air flow path, the first air flow path and the scavenging portare connected at a time when the operating position of the piston comesto a position in which the second air flow path connects the first airflow path and the scavenging port. At this time, since the first airflow path and the scavenging port are arranged on the same plane, it ispossible to achieve a linear arrangement relation from the first airflow path to the scavenging port via the second air flow path.

Accordingly, it is possible to make the flow of the lead air from theair flow path to the scavenging port in a smooth flow state, and it ispossible to make the lead air to flow into the scavenging port from theair flow path in a state of keeping the smooth flow state. Further, itis possible to fill a sufficient amount of lead air into the cylinderfrom the scavenging port. Further, it is possible to keep the entirelength of the piston low and to configure the entire length of theengine low, so that it is possible to configure the engine compact.

If the air flow path and the scavenging port are not arranged on thesame plane, the flow of the lead air from the air flow path to thescavenging port forms a flow curving in a vertical direction.Accordingly, there is generated a problem that it is necessary toelongate the entire length of the piston at an energy loss generated dueto the flow curving in the vertical direction and a degree that the airflow path is formed so as to be curved in the vertical direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational cross sectional view of a stratifiedscavenging two-cycle engine provided with a lead air control apparatusaccording to the present invention.

FIG. 2 is a side elevational cross sectional view of a lead air controlapparatus according to a first embodiment, and corresponds to a crosssectional view along a line A-A in FIG. 3.

FIG. 3 is a plan cross sectional view of the lead air control apparatusaccording to the first embodiment, and corresponds to a cross sectionalview along a line B-B in FIG. 2.

FIG. 4 is a front elevational cross sectional view of a stratifiedscavenging two-cycle engine according to a second embodiment, andcorresponds to a cross sectional view along a line D-D in FIG. 6.

FIG. 5 is a side elevational cross sectional view of the stratifiedscavenging two-cycle engine according to the second embodiment, andcorresponds to a cross sectional view along a line C-C in FIG. 6.

FIG. 6 is a plan cross sectional view of the stratified scavengingtwo-cycle engine according to the second embodiment, and corresponds toa cross sectional view along a line E-E in FIG. 5.

FIG. 7 is a side elevational cross sectional view of a lead air controlapparatus according to a third embodiment.

FIG. 8 is a side elevational cross sectional view of a lead air controlapparatus according to a fourth embodiment.

FIG. 9 is a front elevational cross sectional view of a stratifiedscavenging two-cycle engine provided with a lead air control apparatusaccording to a prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of a lead air control apparatus of a stratifiedscavenging two-cycle engine according to the present invention areexplained with reference to the accompanying drawings. In the meantime,the present invention is not limited to the embodiments described belowand involves a technical region which those skilled in the art caneasily modify based on the embodiments, as a matter of course.

FIG. 1 is a front elevational cross sectional view of a stratifiedscavenging two-cycle engine 1 comprising a lead air control apparatus 20according to the present invention. In FIG. 1, a piston 4 is slidablyfitted to a cylinder 3 attached to an upper portion of a crank case 2,and a crank shaft 5 rotatably attached to the crank case 2 and thepiston 4 are connected by a connecting rod 6.

A spark plug 7 is attached to a top portion of the cylinder 3. A muffler9 is attached to an exhaust port 8 provided on a wall surface of thecylinder 3. A pair of scavenging ports 10, 10 introducing a lead airinto the cylinder are provided at opposing positions in both sidesurfaces having an angle of approximately 90° in a plan view withrespect to the exhaust port 8, in a slightly lower side of the exhaustport 8 provided on the wall surface of the cylinder 3.

The scavenging ports 10, 10 and a crank chamber 11 are connected byscavenging flow paths 12, 12 respectively communicating with a pair ofscavenging ports 10, 10. The scavenging flow paths 12, 12 are formed inthe cylinder 3.

An intake port 13 is provided at a position opposing to the exhaust port8, in a slightly lower side of the scavenging port 10 on the wallsurface of the cylinder 3. A pair of air flow paths 14, 14 respectivelyconnected to the pair of scavenging ports 10, 10 are open in thevicinity of the intake port 13. An insulator 21 aiming at a heatinsulation is attached to an open portion of the intake port 13 and theair flow paths 14, 14, and the insulator 21 is provided with an intakepassage 22 communicating with the intake port 13, and first air passages23, 23 respectively communicating with the pair of air flow paths 14,14.

One end portion of a carburetor 30 is attached to the intake passage 22,and the other end portion of the carburetor 30 is connected to an aircleaner 32. The carburetor 30 is provided with a butterfly type throttlevalve 31 controlling an amount of an air-fuel mixture of an air and afuel. The air cleaner 32 and a pair of first air passages 23, 23 areconnected by a pair of second air passages 24, 24 which are arrangedapproximately in parallel to each other. The respective second airpassages 24, 24 are provided with butterfly type air control valves 25,25 controlling an air amount of the lead air.

The throttle valve 31 and the air control valves 25, 25 are connected bya link apparatus (not shown) or the like, and are configured so as torotate in an interlocking manner. In the meantime, the configurations ofthe throttle valve 31 and the air control valves 25, 25, and theinterlocking mechanism of the throttle valve 31 and the air controlvalves 25, 25 do not exhibit the feature of the present invention, butcan employ the conventionally known configuration and the conventionallyknown interlocking mechanism.

Further, the throttle valve and the air control valve are not limited tothe butterfly type shape, but can employ a throttle valve and an aircontrol valve as far as the valve can control an air flow amount withinthe passage, including a rotary type or the like.

The lead air control apparatus 20 is comprised of the insulator 21, thesecond air passage 24, the air control valve 25, the carburetor 30, thethrottle valve 31 and the air cleaner 32. The air cleaner 32, thecarburetor 30 and the insulator 21 are fastened and attached to thecylinder 3 by bolts 28, 28, and the first air passages 23 and 23 areconnected to the air flow paths 14, 14 provided in the cylinder 3.

Hereinafter, a detailed configuration of the lead air control apparatus20 is explained. FIG. 2 is a side elevational cross sectional view ofthe lead air control apparatus according to a first embodiment and FIG.3 is a plan cross sectional view thereof, in which FIG. 2 is a crosssectional view along a line A-A in FIG. 3 and FIG. 3 is a crosssectional view along a line B-B in FIG. 2.

As shown in FIGS. 2 and 3, a pair of first protruding portions 33, 33integrally formed with the air cleaner 32 are provided in a parallelstate in an upper side of a connection position to the carburetor 30 inthe air cleaner 32. The air control valves 25, 25 are respectivelyprovided in third air passages 26, 26 arranged in the respective firstprotruding portions 33, 33.

The insulator 21 inserted between the carburetor 30 and the cylinder 3for the purpose of insulating the heat is provided with a pair of secondprotruding portions 34, 34 each having the first air passage 23 so as toprotrude toward an obliquely upper side in addition to the intakepassage 22 mentioned above.

The respective first protruding portions 33, 33, and the respectivesecond protruding portions 34, 34 are connected by tubular connectionmembers 35, 35 each having a fourth air passage 27. The insulatorforming the intake passage 22 and the insulator forming the first airpassage 23 may be configured by independent bodies.

A pair of second air passages 24, 24 are configured by the respectivethird air passages 26, 26 and the respective fourth air passages 27, 27.The connection member 35 is manufactured by a material having aflexibility such as a rubber or the like, and the fourth air passage 27is formed in a smooth shape.

Further, step portions 35 a, 35 b are formed in both ends of theconnection member 35. It is possible to connect in a state in which aninner diameter cross sectional area is hardly changed in the respectiveconnection portions between the connection member 35, and the firstprotruding portion 33 and the second protruding portion 34, due to thestep portions 35 a, 35 b formed in both ends of the connection member35.

Since inner peripheral surfaces of expanded portions in the stepportions 35 a, 35 b are closely fitted to outer peripheral surfaces ofthe first protruding portion 33 and the second protruding portion 34, itis possible to execute the connection in an airtight state. Accordingly,it is possible to smoothly and continuously configure the innerperipheral wall between the first air passages 23, 23 and the second airpassages 24, 24 along a length direction of the air passage.

As shown in FIGS. 1 and 2, the air passage of the lead air configured bythe first air passage 23 and the second air passage 24 can be configuredas a downward tilted air passage toward a downstream side in a range ofthe fourth air passage 27 and the first air passage 23 constituted atleast by the connection member 35. Further, it is possible to arrangethe air passage of the lead air configured by the first air passage 23and the second air passage 24 in an upper side of the intake passage 22.

Accordingly, it is possible to set an arrangement relationship in whicha passage direction of the intake passage 22 formed in the insulator 21is differentiated from a passage direction of the first air passage 23.Further, it is possible to form the intake passage 22 at an easilyconnecting position to the carburetor 30 in the insulator 21. Further,it is possible to configure the second protruding portion 34 in thefirst air passage 23 at an arrangement position easily connected by theconnection member 35.

Since the first air passage 23 and the second air passage 24 can beconfigured according to the arrangement relationship mentioned above, itis possible to expand an interval between the connection position of thefirst protruding portion 33 in the air cleaner 32, and the connectionposition of the carburetor 30 and the air cleaner 32, and it is possibleto use a large size air cleaner as the air cleaner.

Accordingly, the large size air cleaner can be used by connecting it toa small size engine in which the intake port 13 for the air-fuel mixtureand the air flow paths 14, 14 for the lead air are arranged at closepositions.

As shown in FIG. 3, a pair of air passages of the lead air configured bythe first air passage 23 and the second air passage 24 can respectivelyarrange the third air passages 26, 26 in the first protruding portions33, 33 and the first air passages 23, 23 in the second protrudingportions 34, 34 in an approximately parallel state.

The respective third air passages 26 and 26 are arranged in anapproximately parallel state to each other, and each of them isrespectively formed as an approximately linear air passage. Further, therespective first air passages 23, 23 are also arranged in anapproximately parallel state to each other, and each of them is formedas an approximately linear air passage.

The approximately linear air passage involves an air passage shape inwhich an inner diameter within the air passage is expanded from anupstream side toward a downstream side, an air passage shape in whichthe inner diameter is inversely compressed from the upstream side towardthe downstream side, and the like, in addition to the air passage inwhich the inner diameter within the air passage is entirely uniform, andincludes all air passage shapes in which a center axial line of the airpassage is formed in an approximately linear shape.

Even if the interval between the pair of first protruding portions 33,33 and the interval between the second protruding portions 34, 34 aredifferent, it is possible to configure the portion between the secondair passage 24 and the first air passage 23 as a smooth pipe passageshape, by connecting and communicating by a pair of connection members35, 35 having the flexibility.

Accordingly, it is possible to reduce a pipe passage resistance in theair passage from the second air passage 24 to the first air passage 23,and it is possible to circulate the lead air having a small pressureloss. Therefore, it is possible to sufficiently secure the air amount ofthe lead air supplied into the engine.

Further, it is possible to increase a freedom with respect to a placewhich can be selected as the forming position of a pair of firstprotruding portions 33, 33 integrally formed with the air cleaner 32 andthe third air passages 26, 26, and the forming position of the first airpassages 23, 23 in the insulator 21.

Accordingly, it is possible to make the configurations of the insulatorsimple. Further, it is possible to configure the arrangementrelationship of the pair of first protruding portions 33, 33 and thepair of second protruding portions 34, 34 as a simple arrangementrelationship. As a result, it is possible to simplify the configurationsof the entire stratified scavenging two-cycle engine, and it is possibleto configure the engine compact. Further, it is possible to configurethe air passage of the lead air as a smooth air passage having a smallair resistance.

Next, an operation is explained. At a top dead center position of thepiston 4 shown in FIG. 1, the air-fuel mixture of the air and the fuelis compressed in an upper portion of the cylinder chamber, and isignited by the spark plug 7, whereby the air-fuel mixture is exploded soas to push down the piston 4. At this time, the scavenging port 10 andthe scavenging flow path 12 is filled with a clean air introducedthereto from the air cleaner 32 via the second air passage 24, thesecond air passage 23 and the air flow passage 14.

Further, the crank chamber 11 is filled with the air-fuel mixtureobtained by mixing the air from the air cleaner 32 with the fuel by thecarburetor 30. When the piston 4 moves downward, the intake port 13 isfirst closed, and the air-fuel mixture filled in the crank chamber 11 iscompressed. Next, the exhaust port 8 is opened, and the exhaust gas isdischarged to an exterior portion from the exhaust port 8 via themuffler 9.

Successively, the scavenging port 10 is opened, the lead air within thescavenging port 10 and the scavenging flow path 12 flows into thecylinder 3 by the compressed pressure within the crank chamber 11, andthe remaining exhaust gas is discharged from the exhaust port 8.Thereafter, the air-fuel mixture within the crank chamber 11 flows intothe cylinder 3 chamber, however, since the piston 4 is in the process ofascending stroke at this time, and the exhaust port 8 is made in aclosed state by the piston 4, there is no risk that the air-fuel mixtureis discharged to the external portion.

An amount of the air-fuel mixture passing through the carburetor 30 iscontrolled by the throttle valve 31, and the air amount of the lead airpassing through the second air passage 24 is controlled by the aircontrol valve 25. Further, since the throttle valve 31 works with theair control valve 25, it is possible to always keep a balance betweenthe amount of the air-fuel mixture and the air amount of the lead air,an optimum supply is executed and the combustion in an optimum state isexecuted.

The lead air control apparatus of the stratified scavenging two-cycleengine according to the present invention is configured such that a pairof air passages are arranged in a parallel state, and the air controlvalve is provided in each of them. Accordingly, it is not necessary tobranch the air passage into the right and left sides in the insulatorportion as is different from the conventional configuration, and it ispossible to simplify the configuration in the insulator portion.

Further, since it is possible to form the air passage connecting the aircleaner to the air flow path connected to the scavenging port of theengine as the smooth shape, it is possible to reduce the air resistancewithin the air passage, and it is possible to improve an engineperformance.

Further, it is possible to make the first air passage formed in theinsulator as the linear simple configuration, and it is possible toconfigure the passage length of the first air passage short.Accordingly, it is possible to configure an entire length L of theengine shown in FIG. 1 shorter than an entire length M of theconventional engine shown in FIG. 6, and it is possible to configure theentire of the engine compact.

Further, the insulator 21 can be provided with the pair of secondprotruding portions 34, 34 each having the first air passage 23 so as toprotrude in the obliquely upward shape. Accordingly, it is possible toarrange the air outlet in the intake passage for the air-fuel mixtureand the air outlet for the lead air so as to be formed at the largeapart positions. The large size air cleaner can be used as the aircleaner.

Accordingly, the large size air cleaner can be connected to the smallsize engine in which the intake port 13 for the air-fuel mixture and theair flow paths 14, 14 for the lead air are formed at the close position.

Further, the first air passage 23 and the second air passage can beeasily assembled by using the connection member having the flexibilityas the connection member 35, and the assembled air passage can be easilyformed as the passage having a small air resistance.

Since the step portions 35 a, 35 b are formed in both ends of theconnection member 35, it is possible to connect in a state in which theinner diameter cross sectional area is hardly changed in the connectionportion between the connection member 35, and the first protrudingportion 33 and the second protruding portion 34. Accordingly, it ispossible to reduce the pressure loss caused by the inner diameter crosssectional area in the connection portion.

FIGS. 4 to 6 show a configuration of a stratified scavenging two-cycleengine according to a second embodiment of the present invention. FIG. 4is a front elevational cross sectional view of the stratified scavengingtwo-cycle engine, and corresponds to a cross sectional view along a lineD-D in FIG. 6. FIG. 5 is a side elevational cross sectional view of thestratified scavenging two-cycle engine, and corresponds to acrosssectional view along a line C-C in FIG. 6. Further, FIG. 6 is a plancross sectional view of the stratified scavenging two-cycle engine, andcorresponds to a cross sectional view along a line E-E in FIG. 5.

A description of the same portion is not repeated by using the samereference numerals as those of the same portion in the first embodiment,and only different portions is explained. As shown in FIGS. 4 and 5, theintake passage 22 is communicated with the intake port 13 formed in thecylinder 3, and the intake port 13 is communicated with the crankchamber 11.

As shown in FIGS. 5 and 6, the first air passage 23 formed in theinsulator 21 is communicated with a first air flow path 14 a formed inthe cylinder 3. The first air flow path 14 a is communicated with asecond air flow path 14 b formed on an outer peripheral surface of thepiston 4 via a lead air port 14 d formed on the outer peripheral surfaceof the piston 4.

The lead air port 14 d is configured as a part of the second air flowpath 14 b, and the second air flow path 14 b is configured as a shapesurrounded by a piston groove wall 14 c. The second air flow path 14 bis communicated with third air flow paths 18 a, 18 b formed in thecylinder 3. The third air passages 18 a, 18 b are respectivelycommunicated with the scavenging port 10, and are communicated with thecrank chamber 11.

The scavenging ports 10 respectively communicating with the third airpassages 18 a, 18 b can be arranged at different positions on the innerperipheral surface of the cylinder 3, can be arranged at adjacentpositions, or can be arranged as the same scavenging port 10.

As shown in FIG. 5, the first air flow path 14 a and the scavenging port10 are arranged so as to be connectable on the same plane via the secondair flow path 14 b. When the piston 4 is actuated and the first air flowpath 14 a, the second air flow path 14 b and the scavenging port 10 arearranged in an approximately linear shape, the lead air can flow intothe scavenging port 10 from the first air flow passage 14 a through thesecond air flow path 14 b which are arranged in the approximately linearshape. Accordingly, it is possible to charge the lead air having a smallpassage resistance and a sufficient amount from the scavenging port 10into the cylinder 3 or the like.

As shown in FIG. 6, a pair of first air passages 23 and 23 are formed inthe insulator 21. As mentioned above, a pair of first air passages 23,23 are respectively branched by the third air flow paths 18 a, 18 b, andare respectively communicated with two sets of left and right scavengingports 10 which are arranged symmetrically within the cylinder chamber.

Two sets of right and left scavenging ports 10 are not limited to beformed in two right and left positions within the cylinder chamber, butcan be arranged at a necessary number. In the case of placing anecessary number of scavenging ports, the scavenging port can be simplyconfigured by arranging a necessary number of third air flow paths 18which are branched from the second air flow path 14 b formed in thepiston 4 and formed in the cylinder 3.

It is easy to arrange the first air flow path 14 a in a parallel state,by forming the second air flow path 14 b on the outer peripheral surfaceof the piston 4. Accordingly, it is possible to arrange a pair of firstair passages 23 communicating with a pair of first air flow paths 14 ain a parallel state which is approximately equal to the first air flowpaths 14 a, and it is easy to form the first air flow path 14 a and thefirst air passage 23 in an approximately linear shape.

As shown in FIGS. 5 and 6, seal members 16 a, 16 b may be interposed inthe connection between the step portions 35 a, 35 b of the connectionmember 35, and the first protruding portion 33 and the second protrudingportion 34. A pair of connection members 35, 35 can be integrallyconfigured therebetween via the connection member 17, or the connectionmembers 35, 35 can be independently configured as separated bodies.

Since a pair of connection members 35, 35 are integrally configuredtherebetween via the connection member 17, it is possible to arrange theair passage of the lead air and the intake passage communicating withthe carburetor 30 as independent passages which are different in avertical direction.

Accordingly, the air passage of the lead air and the intake passage 22can be configured with a neat arrangement relationship and with acompact configuration, without arranging the air passage of the lead airin both sides of the carburetor 30 or without employing the arrangementrelationship that the air passage of the lead air and the intake passage22 cross.

Since the air passage of the lead air and the intake passage 22 areconfigured as the neat arrangement relationship, it is possible to makethe configuration of the lead air control apparatus 20 compact.

As shown in FIGS. 5 and 6, since it is possible to form a pair of firstair flow paths 14 a, 14 a and a pair of first air passages 23, 23 in anapproximately linear shape in an approximately parallel state, it ispossible to configure the first air flow paths 14 a, 14 a and the intakeport 13 in a state in which the arranged positions thereof are close toeach other. Further, the air cleaner 32 can be connected to the firstair passage 23 via the connection member 35 and in the smooth flow pathshape. Accordingly, the large size air cleaner 32 can be connected in areduced air resistance state even to the small size engine serving asthe stratified scavenging two-cycle engine.

FIG. 7 is a side elevational cross sectional view of a lead air controlapparatus 20 a according to a third embodiment of the present invention.A description of the same portion is not repeated by using the samereference numerals to the same portions as those of the firstembodiment, and only different portions is explained.

The third embodiment is configured different from the first embodimentin a point that the first protruding portion 33 integrally formed withthe air cleaner 32 in the first embodiment is configured as a firstprotruding portion 33 a which is independent from an air cleaner 32 a.The other configurations are the same as those of the first embodiment.

As shown in FIG. 7, a pair of first protruding portions 33 a areattached while holding a joint member 36 interposed between the aircleaner 32 a and a carburetor 30 a. The air control valve 25 is providedin the first protruding portion 33 a. Accordingly, it is possible tosimplify the shape of the air cleaner, and it is possible to reduce acost. Further, a connection portion between both end portions of a pairof first protruding portions 33 a and the air cleaner 32 a, and aconnection portion to the connection member 35 are respectivelyconnected in a state in which a change in an inner diameter crosssectional area in the connection portions is hardly generated.

FIG. 8 is a side elevational cross sectional view of a lead air controlapparatus 20 b according to a fourth embodiment of the presentinvention. A description of the same portions is not repeated by usingthe same reference numerals to the same portions in the firstembodiment, and only different portions is explained.

In the fourth embodiment, an air passage pipe 37 corresponding to thefirst protruding portion 33 a in the third embodiment is formed in adifferent way from the second embodiment. In the third embodiment, thefirst protruding portion 33 a is configured such as to be formed in thejoint member 36 interposed between the air cleaner 32 a and thecarburetor 30 a. On the contrary, in the fourth embodiment, the airpassage pipe 37 is formed in an air passage member 39 which isintegrally formed with a bracket 38 firmly fixed to an upper portion ofthe carburetor 30 b. The other configurations are the same as those ofthe first to third embodiments.

In FIG. 8, the air passage member 39 integrally forming a pair of airpassage pipes 37 and the bracket 38 is firmly fixed to the upper portionof the carburetor 30 b by bolts (not shown). The air cleaner 32 b andthe air passage pipe 37 are connected based on a faucet joint. An O-ring(not shown) is inserted to the faucet portion so as to keep anairtightness. The air control valve 25 is provided in the air passagepipe 37. Further, a connection portion between both end portions of apair of air passage members 39 and the air cleaner 32 a, and aconnection portion to the connection member 35 are connected in a statein which a change in an inner diameter cross sectional area in theconnection portions is hardly generated.

Accordingly, it is possible to simplify the shape of the air cleaner,and it is possible to reduce a cost.

The lead air control apparatus according to the present invention may beconfigured as described below in addition to the configurationsmentioned above. The connection member is constituted by a pair oftubular member, but may be configured such that two air passages areprovided in one member, and the material thereof may employ a metal or asynthetic resin in addition to the rubber.

1. A lead air control apparatus of a stratified scavenging two-cycleengine, the stratified scavenging two-cycle engine comprising: acarburetor (30) connected to an air cleaner (32, 32 a, 32 b) and havinga throttle valve (31); an insulator (21) inserted between the carburetor(30) and a cylinder (3) for a purpose of insulating heat; and an intakepassage (22) formed in the insulator (21) and connecting between anintake port (13) provided in the cylinder (3) and the carburetor (30),characterized in that the apparatus comprises: a pair of first airpassages (23, 23) formed in the insulator (21), and respectivelyconnected to a pair of scavenging ports (10, 10) provided in thecylinder (3); a pair of second air passages (24, 24) respectivelyconnecting between the air cleaner (32, 32 a, 32 b) and the respectivefirst air passages (23, 23), and arranged in an approximately parallelstate; and air control valves (25, 25) provided in the respective secondair passages (24, 24), and controlling an air amount of a lead air forscavenging.
 2. The lead air control apparatus of the stratifiedscavenging two-cycle engine according to claim 1, characterized in thatthe air control valves (25, 25) are provided near the air cleaner (32,32 a, 32 b) or are integrally formed with the air cleaner (32, 32 a, 32b); the respective second air passages (24, 24) are provided withconnection members (35, 35) respectively connected to the first airpassages (23, 23); and an inner peripheral wall from each of the firstair passages (23, 23) to each of the second air passages (24, 24) isformed smoothly and continuously along a length direction of the airpassages.
 3. The lead air control apparatus of the stratified scavengingtwo-cycle engine according to claim 2, characterized in that aconnection portion in an end portion of each of the connection members(35, 35) is formed such that a change of an internal diameter crosssectional area between the connection portion and a connected portion issmall.
 4. The lead air control apparatus of the stratified scavengingtwo-cycle engine according to claim 2 or 3, characterized in that eachof the connection members (35, 35) has a flexibility.
 5. The lead aircontrol apparatus of the stratified scavenging two-cycle engineaccording to any one of claims 1 to 4, characterized in that therespective first air passages (23, 23) are arranged so as to beapproximately parallel to each other, and each of the first air passagesis formed as an approximately linear air passage.
 6. The lead aircontrol apparatus of the stratified scavenging two-cycle engineaccording to any one of claims 1 to 5, characterized in that therespective first air passages (23, 23) have air flow paths (14, 14)formed within the cylinder (3); and the pair of air flow paths (14, 14)and the pair of scavenging ports (10, 10) are arranged so as to beconnectable on a same plane.